Conventionally, in various image forming devices, such as printers, facsimiles, copiers, plotters, and multi-function peripherals, a liquid discharge head which discharges a liquid to a recording medium is installed to form an image on the recording medium.
In the following, the liquid discharge device means a device which discharges drops of a liquid to a recording medium. The recording medium may be paper, yarn, fiber, textile, leather, metal, plastic, glass, wood, ceramics, etc. The recording medium is also called a printing medium, a copy sheet, etc., and these are used as the synonym irrespective of the kind of the material. The term “recording” means not only creating a meaningful image, such as characters and figures, on the recording medium, but also creating a meaningless image, such as a pattern, on the recording medium. Recording is also called image formation or printing, and these are also used as the synonym.
An ink jet head is an example of the liquid discharge head, and specifically a piezoelectric type ink jet head is well known. In the piezoelectric type ink jet head, a piezoelectric element is used as a pressure generating unit for generating a pressure which pressurizes an ink (or the liquid) in the liquid chamber. Especially, a laminated type piezoelectric element in which a piezoelectric layer and an internal electrode are laminated is used. With the laminated type piezoelectric element being driven, a resilient diaphragm which forms the surface of a wall of the liquid chamber is elastically deformed by a displacement in the d33 or d31 direction of the piezoelectric element, and changes the internal capacity/pressure of the liquid chamber so that an ink drop is discharged from the nozzle of the ink jet head.
For example, Japanese Patent No. 3114771 discloses an ink jet head using such a laminated type piezoelectric element. In the ink jet head of this document, the piezoelectric layers and the internal electrodes are alternately laminated to form the laminated type piezoelectric element (driver element block). At end portions of the laminated type piezoelectric element, the individual external electrodes and the common external electrodes are formed. Slot processing of the laminated type piezoelectric element is performed by leaving a part thereof, so that a plurality of actuation parts (drive channels) in the center thereof and non-actuation parts at both ends thereof are formed. In operation, the laminated type piezoelectric element generates the pressure which pressurizes the liquid in the liquid chamber by a displacement in the d31 direction of the laminated type piezoelectric element. The common electrodes of this laminated type piezoelectric element are taken from the non-actuation parts at the both ends in the row direction of the actuation parts.
Moreover, Japanese Laid-Open Patent Application No. 2003-250281 discloses an ink jet head which uses the displacement in the d33 direction of a laminated type piezoelectric element. In the ink jet head of this document, slot processing of the piezoelectric element bonded to the base surface is performed, and the individual piezoelectric elements corresponding to the liquid chambers with which the nozzles communicate are formed.
Moreover, Japanese Laid-Open Patent Application No. 06-198877 discloses a line type ink jet head. In the line type ink jet head of this document, a plurality of nozzle openings are arranged on a single continuous nozzle plate to form the nozzle plate. The piezoelectric elements are disposed to face the corresponding nozzle openings by processing of a plurality of bulk piezoelectric crystals, and the boundary portion of the adjoining bulk piezoelectric crystals is the processing region.
In recent years, the ink-jet recording device as an image forming device is demanded for high-speed printing. The methods for achieving high-speed printing of the ink-jet recording device may include a method of increasing the ink discharge frequency, and a method of increasing the number of nozzles. However, if the ink discharge frequency is increased, it is necessary to move the head carriage in the ink-jet recording device at high speed corresponding to the increased ink discharge frequency. It is difficult to control the powerful motor with sufficient accuracy and perform the ink discharging at high frequency with good stability.
To eliminate the problems, the use of an elongated head, such as a line, in which the length of the head is lengthened and the number of nozzles is increased, is taken into consideration. However, in order to lengthen the length of the head with the head configuration as in Japanese Patent No. 3114771 or Japanese Laid-Open Patent Application No. 2003-250281 used, it is necessary to lengthen the length of each of the component parts of the head. Since the piezoelectric element, such as PZT, is a very slender long part, enlarging the length of the head will cause the difficulty in respect of the manufacturing process or handling of the piezoelectric element.
Moreover, in the case of the line type ink jet head of Japanese Laid-Open Patent Application No. 06-198877, the plurality of bulk piezoelectric crystals must be divided into the piezoelectric elements. Since slanting or chipping of the piezoelectric elements is likely to arise, the yield worsens and the manufacturing cost becomes high.